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                    插件开发：平台通道简介
            
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                    插件开发：实现Android端API
            
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                    插件开发：实现IOS端API
            
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                    国际化
            
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                    让App支持多语言
            
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                    实现Localizations
            
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                    使用Intl包
            
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                    Flutter核心原理
            
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                    Element和BuildContext
            
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                                <h1 id="element&#x4E0E;buildcontext">Element&#x4E0E;BuildContext</h1>
<h3 id="element">Element</h3>
<p>&#x5728;&#x201C;Widget&#x7B80;&#x4ECB;&#x201D;&#x4E00;&#x8282;&#xFF0C;&#x6211;&#x4EEC;&#x4ECB;&#x7ECD;&#x4E86;Widget&#x548C;Element&#x7684;&#x5173;&#x7CFB;&#xFF0C;&#x6211;&#x4EEC;&#x77E5;&#x9053;&#x6700;&#x7EC8;&#x7684;UI&#x6811;&#x5176;&#x5B9E;&#x662F;&#x7531;&#x4E00;&#x4E2A;&#x4E2A;&#x72EC;&#x7ACB;&#x7684;Element&#x8282;&#x70B9;&#x6784;&#x6210;&#x3002;&#x6211;&#x4EEC;&#x4E5F;&#x77E5;&#x9053;&#x4E86;&#x7EC4;&#x4EF6;&#x6700;&#x7EC8;&#x7684;Layout&#x3001;&#x6E32;&#x67D3;&#x90FD;&#x662F;&#x901A;&#x8FC7;RenderObject&#x6765;&#x5B8C;&#x6210;&#x7684;&#xFF0C;&#x4ECE;&#x521B;&#x5EFA;&#x5230;&#x6E32;&#x67D3;&#x7684;&#x5927;&#x4F53;&#x6D41;&#x7A0B;&#x662F;&#xFF1A;&#x6839;&#x636E;Widget&#x751F;&#x6210;Element&#xFF0C;&#x7136;&#x540E;&#x521B;&#x5EFA;&#x76F8;&#x5E94;&#x7684;RenderObject&#x5E76;&#x5173;&#x8054;&#x5230;Element.renderObject&#x5C5E;&#x6027;&#x4E0A;&#xFF0C;&#x6700;&#x540E;&#x518D;&#x901A;&#x8FC7;RenderObject&#x6765;&#x5B8C;&#x6210;&#x5E03;&#x5C40;&#x6392;&#x5217;&#x548C;&#x7ED8;&#x5236;&#x3002;</p>
<p>Element&#x5C31;&#x662F;Widget&#x5728;UI&#x6811;&#x5177;&#x4F53;&#x4F4D;&#x7F6E;&#x7684;&#x4E00;&#x4E2A;&#x5B9E;&#x4F8B;&#x5316;&#x5BF9;&#x8C61;&#xFF0C;&#x5927;&#x591A;&#x6570;Element&#x53EA;&#x6709;&#x552F;&#x4E00;&#x7684;renderObject&#xFF0C;&#x4F46;&#x8FD8;&#x6709;&#x4E00;&#x4E9B;Element&#x4F1A;&#x6709;&#x591A;&#x4E2A;&#x5B50;&#x8282;&#x70B9;&#xFF0C;&#x5982;&#x7EE7;&#x627F;&#x81EA;RenderObjectElement&#x7684;&#x4E00;&#x4E9B;&#x7C7B;&#xFF0C;&#x6BD4;&#x5982;MultiChildRenderObjectElement&#x3002;&#x6700;&#x7EC8;&#x6240;&#x6709;Element&#x7684;RenderObject&#x6784;&#x6210;&#x4E00;&#x68F5;&#x6811;&#xFF0C;&#x6211;&#x4EEC;&#x79F0;&#x4E4B;&#x4E3A;&#x6E32;&#x67D3;&#x6811;&#xFF0C;&#x5373;render tree&#x3002;</p>
<p>Element&#x7684;&#x751F;&#x547D;&#x5468;&#x671F;&#x5982;&#x4E0B;&#xFF1A;</p>
<ol>
<li>Framework &#x8C03;&#x7528;<code>Widget.createElement</code> &#x521B;&#x5EFA;&#x4E00;&#x4E2A;Element&#x5B9E;&#x4F8B;&#xFF0C;&#x8BB0;&#x4E3A;<code>element</code></li>
<li>Framework &#x8C03;&#x7528; <code>element.mount(parentElement,newSlot)</code> &#xFF0C;mount&#x65B9;&#x6CD5;&#x4E2D;&#x9996;&#x5148;&#x8C03;&#x7528;<code>elment</code>&#x6240;&#x5BF9;&#x5E94;Widget&#x7684;<code>createRenderObject</code>&#x65B9;&#x6CD5;&#x521B;&#x5EFA;&#x4E0E;<code>element</code>&#x76F8;&#x5173;&#x8054;&#x7684;RenderObject&#x5BF9;&#x8C61;&#xFF0C;&#x7136;&#x540E;&#x8C03;&#x7528;<code>element.attachRenderObject</code>&#x65B9;&#x6CD5;&#x5C06;<code>element.renderObject</code>&#x6DFB;&#x52A0;&#x5230;&#x6E32;&#x67D3;&#x6811;&#x4E2D;&#x63D2;&#x69FD;&#x6307;&#x5B9A;&#x7684;&#x4F4D;&#x7F6E;&#xFF08;&#x8FD9;&#x4E00;&#x6B65;&#x4E0D;&#x662F;&#x5FC5;&#x987B;&#x7684;&#xFF0C;&#x4E00;&#x822C;&#x53D1;&#x751F;&#x5728;Element&#x6811;&#x7ED3;&#x6784;&#x53D1;&#x751F;&#x53D8;&#x5316;&#x65F6;&#x624D;&#x9700;&#x8981;&#x91CD;&#x65B0;attach&#xFF09;&#x3002;&#x63D2;&#x5165;&#x5230;&#x6E32;&#x67D3;&#x6811;&#x540E;&#x7684;<code>element</code>&#x5C31;&#x5904;&#x4E8E;&#x201C;active&#x201D;&#x72B6;&#x6001;&#xFF0C;&#x5904;&#x4E8E;&#x201C;active&#x201D;&#x72B6;&#x6001;&#x540E;&#x5C31;&#x53EF;&#x4EE5;&#x663E;&#x793A;&#x5728;&#x5C4F;&#x5E55;&#x4E0A;&#x4E86;&#xFF08;&#x53EF;&#x4EE5;&#x9690;&#x85CF;&#xFF09;&#x3002;</li>
<li>&#x5F53;<code>element</code>&#x7236;Widget&#x7684;&#x914D;&#x7F6E;&#x6570;&#x636E;&#x6539;&#x53D8;&#x65F6;&#xFF0C;&#x4E3A;&#x4E86;&#x8FDB;&#x884C;Element&#x590D;&#x7528;&#xFF0C;Framework&#x5728;&#x51B3;&#x5B9A;&#x91CD;&#x65B0;&#x521B;&#x5EFA;Element&#x524D;&#x4F1A;&#x5148;&#x5C1D;&#x8BD5;&#x590D;&#x7528;&#x76F8;&#x540C;&#x4F4D;&#x7F6E;&#x65E7;&#x7684;element&#xFF1A;&#x8C03;&#x7528;Element&#x5BF9;&#x5E94;Widget&#x7684;<code>canUpdate()</code>&#x65B9;&#x6CD5;&#xFF0C;&#x5982;&#x679C;&#x8FD4;&#x56DE;<code>true</code>&#xFF0C;&#x5219;&#x590D;&#x7528;&#x65E7;Element&#xFF0C;&#x65E7;&#x7684;Element&#x4F1A;&#x4F7F;&#x7528;&#x65B0;&#x7684;Widget&#x914D;&#x7F6E;&#x6570;&#x636E;&#x66F4;&#x65B0;&#xFF0C;&#x53CD;&#x4E4B;&#x5219;&#x4F1A;&#x521B;&#x5EFA;&#x4E00;&#x4E2A;&#x65B0;&#x7684;Element&#xFF0C;&#x4E0D;&#x4F1A;&#x590D;&#x7528;&#x3002;<code>Widget.canUpdate()</code>&#x4E3B;&#x8981;&#x662F;&#x5224;&#x65AD;<code>newWidget</code>&#x4E0E;<code>oldWidget</code>&#x7684;<code>runtimeType</code>&#x548C;<code>key</code>&#x662F;&#x5426;&#x540C;&#x65F6;&#x76F8;&#x7B49;&#xFF0C;&#x5982;&#x679C;&#x540C;&#x65F6;&#x76F8;&#x7B49;&#x5C31;&#x8FD4;&#x56DE;<code>true</code>&#xFF0C;&#x5426;&#x5219;&#x5C31;&#x4F1A;&#x8FD4;&#x56DE;<code>false</code>&#x3002;&#x6839;&#x636E;&#x8FD9;&#x4E2A;&#x539F;&#x7406;&#xFF0C;&#x5F53;&#x6211;&#x4EEC;&#x9700;&#x8981;&#x5F3A;&#x5236;&#x66F4;&#x65B0;&#x4E00;&#x4E2A;Widget&#x65F6;&#xFF0C;&#x53EF;&#x4EE5;&#x901A;&#x8FC7;&#x6307;&#x5B9A;&#x4E0D;&#x540C;&#x7684;Key&#x6765;&#x7981;&#x6B62;&#x590D;&#x7528;&#x3002;</li>
<li>&#x5F53;&#x6709;&#x7236;Widget&#x7684;&#x914D;&#x7F6E;&#x6570;&#x636E;&#x6539;&#x53D8;&#x65F6;&#xFF0C;&#x540C;&#x65F6;&#x5176;<code>State.build</code>&#x8FD4;&#x56DE;&#x7684;Widget&#x7ED3;&#x6784;&#x4E0E;&#x4E4B;&#x524D;&#x4E0D;&#x540C;&#xFF0C;&#x6B64;&#x65F6;&#x5C31;&#x9700;&#x8981;&#x91CD;&#x65B0;&#x6784;&#x5EFA;&#x5BF9;&#x5E94;&#x7684;Element&#x6811;&#x3002;&#x4E3A;&#x4E86;&#x8FDB;&#x884C;Element&#x590D;&#x7528;&#xFF0C;&#x5728;Element&#x91CD;&#x65B0;&#x6784;&#x5EFA;&#x524D;&#x4F1A;&#x5148;&#x5C1D;&#x8BD5;&#x662F;&#x5426;&#x53EF;&#x4EE5;&#x590D;&#x7528;&#x65E7;&#x6811;&#x4E0A;&#x76F8;&#x540C;&#x4F4D;&#x7F6E;&#x7684;element&#xFF0C;element&#x8282;&#x70B9;&#x5728;&#x66F4;&#x65B0;&#x524D;&#x90FD;&#x4F1A;&#x8C03;&#x7528;&#x5176;&#x5BF9;&#x5E94;Widget&#x7684;<code>canUpdate</code>&#x65B9;&#x6CD5;&#xFF0C;&#x5982;&#x679C;&#x8FD4;&#x56DE;<code>true</code>&#xFF0C;&#x5219;&#x590D;&#x7528;&#x65E7;Element&#xFF0C;&#x65E7;&#x7684;Element&#x4F1A;&#x4F7F;&#x7528;&#x65B0;Widget&#x914D;&#x7F6E;&#x6570;&#x636E;&#x66F4;&#x65B0;&#xFF0C;&#x53CD;&#x4E4B;&#x5219;&#x4F1A;&#x521B;&#x5EFA;&#x4E00;&#x4E2A;&#x65B0;&#x7684;Element&#x3002;<code>Widget.canUpdate</code>&#x4E3B;&#x8981;&#x662F;&#x5224;&#x65AD;<code>newWidget</code>&#x4E0E;<code>oldWidget</code>&#x7684;<code>runtimeType</code>&#x548C;<code>key</code>&#x662F;&#x5426;&#x540C;&#x65F6;&#x76F8;&#x7B49;&#xFF0C;&#x5982;&#x679C;&#x540C;&#x65F6;&#x76F8;&#x7B49;&#x5C31;&#x8FD4;&#x56DE;<code>true</code>&#xFF0C;&#x5426;&#x5219;&#x5C31;&#x4F1A;&#x8FD4;&#x56DE;<code>false</code>&#x3002;&#x6839;&#x636E;&#x8FD9;&#x4E2A;&#x539F;&#x7406;&#xFF0C;&#x5F53;&#x6211;&#x4EEC;&#x9700;&#x8981;&#x5F3A;&#x5236;&#x66F4;&#x65B0;&#x4E00;&#x4E2A;Widget&#x65F6;&#xFF0C;&#x53EF;&#x4EE5;&#x901A;&#x8FC7;&#x6307;&#x5B9A;&#x4E0D;&#x540C;&#x7684;Key&#x6765;&#x907F;&#x514D;&#x590D;&#x7528;&#x3002;</li>
<li>&#x5F53;&#x6709;&#x7956;&#x5148;Element&#x51B3;&#x5B9A;&#x8981;&#x79FB;&#x9664;<code>element</code> &#x65F6;&#xFF08;&#x5982;Widget&#x6811;&#x7ED3;&#x6784;&#x53D1;&#x751F;&#x4E86;&#x53D8;&#x5316;&#xFF0C;&#x5BFC;&#x81F4;<code>element</code>&#x5BF9;&#x5E94;&#x7684;Widget&#x88AB;&#x79FB;&#x9664;&#xFF09;&#xFF0C;&#x8FD9;&#x65F6;&#x8BE5;&#x7956;&#x5148;Element&#x5C31;&#x4F1A;&#x8C03;&#x7528;<code>deactivateChild</code> &#x65B9;&#x6CD5;&#x6765;&#x79FB;&#x9664;&#x5B83;&#xFF0C;&#x79FB;&#x9664;&#x540E;<code>element.renderObject</code>&#x4E5F;&#x4F1A;&#x88AB;&#x4ECE;&#x6E32;&#x67D3;&#x6811;&#x4E2D;&#x79FB;&#x9664;&#xFF0C;&#x7136;&#x540E;Framework&#x4F1A;&#x8C03;&#x7528;<code>element.deactivate</code> &#x65B9;&#x6CD5;&#xFF0C;&#x8FD9;&#x65F6;<code>element</code>&#x72B6;&#x6001;&#x53D8;&#x4E3A;&#x201C;inactive&#x201D;&#x72B6;&#x6001;&#x3002;</li>
<li>&#x201C;inactive&#x201D;&#x6001;&#x7684;element&#x5C06;&#x4E0D;&#x4F1A;&#x518D;&#x663E;&#x793A;&#x5230;&#x5C4F;&#x5E55;&#x3002;&#x4E3A;&#x4E86;&#x907F;&#x514D;&#x5728;&#x4E00;&#x6B21;&#x52A8;&#x753B;&#x6267;&#x884C;&#x8FC7;&#x7A0B;&#x4E2D;&#x53CD;&#x590D;&#x521B;&#x5EFA;&#x3001;&#x79FB;&#x9664;&#x67D0;&#x4E2A;&#x7279;&#x5B9A;element&#xFF0C;&#x201C;inactive&#x201D;&#x6001;&#x7684;element&#x5728;&#x5F53;&#x524D;&#x52A8;&#x753B;&#x6700;&#x540E;&#x4E00;&#x5E27;&#x7ED3;&#x675F;&#x524D;&#x90FD;&#x4F1A;&#x4FDD;&#x7559;&#xFF0C;&#x5982;&#x679C;&#x5728;&#x52A8;&#x753B;&#x6267;&#x884C;&#x7ED3;&#x675F;&#x540E;&#x5B83;&#x8FD8;&#x672A;&#x80FD;&#x91CD;&#x65B0;&#x53D8;&#x6210;&#x201D;active&#x201C;&#x72B6;&#x6001;&#xFF0C;Framework&#x5C31;&#x4F1A;&#x8C03;&#x7528;&#x5176;<code>unmount</code>&#x65B9;&#x6CD5;&#x5C06;&#x5176;&#x5F7B;&#x5E95;&#x79FB;&#x9664;&#xFF0C;&#x8FD9;&#x65F6;element&#x7684;&#x72B6;&#x6001;&#x4E3A;<code>defunct</code>,&#x5B83;&#x5C06;&#x6C38;&#x8FDC;&#x4E0D;&#x4F1A;&#x518D;&#x88AB;&#x63D2;&#x5165;&#x5230;&#x6811;&#x4E2D;&#x3002;</li>
<li>&#x5982;&#x679C;<code>element</code>&#x8981;&#x91CD;&#x65B0;&#x63D2;&#x5165;&#x5230;Element&#x6811;&#x7684;&#x5176;&#x5B83;&#x4F4D;&#x7F6E;&#xFF0C;&#x5982;<code>element</code>&#x6216;<code>element</code>&#x7684;&#x7956;&#x5148;&#x62E5;&#x6709;&#x4E00;&#x4E2A;GlobalKey&#xFF08;&#x7528;&#x4E8E;&#x5168;&#x5C40;&#x590D;&#x7528;&#x5143;&#x7D20;&#xFF09;&#xFF0C;&#x90A3;&#x4E48;Framework&#x4F1A;&#x5148;&#x5C06;element&#x4ECE;&#x73B0;&#x6709;&#x4F4D;&#x7F6E;&#x79FB;&#x9664;&#xFF0C;&#x7136;&#x540E;&#x518D;&#x8C03;&#x7528;&#x5176;<code>activate</code>&#x65B9;&#x6CD5;&#xFF0C;&#x5E76;&#x5C06;&#x5176;<code>renderObject</code>&#x91CD;&#x65B0;attach&#x5230;&#x6E32;&#x67D3;&#x6811;&#x3002;</li>
</ol>
<p>&#x770B;&#x5B8C;Element&#x7684;&#x751F;&#x547D;&#x5468;&#x671F;&#xFF0C;&#x53EF;&#x80FD;&#x6709;&#x4E9B;&#x8BFB;&#x8005;&#x4F1A;&#x6709;&#x7591;&#x95EE;&#xFF0C;&#x5F00;&#x53D1;&#x8005;&#x4F1A;&#x76F4;&#x63A5;&#x64CD;&#x4F5C;Element&#x6811;&#x5417;&#xFF1F;&#x5176;&#x5B9E;&#x5BF9;&#x4E8E;&#x5F00;&#x53D1;&#x8005;&#x6765;&#x8BF4;&#xFF0C;&#x5927;&#x591A;&#x6570;&#x60C5;&#x51B5;&#x4E0B;&#x53EA;&#x9700;&#x8981;&#x5173;&#x6CE8;Widget&#x6811;&#x5C31;&#x884C;&#xFF0C;Flutter&#x6846;&#x67B6;&#x5DF2;&#x7ECF;&#x5C06;&#x5BF9;Widget&#x6811;&#x7684;&#x64CD;&#x4F5C;&#x6620;&#x5C04;&#x5230;&#x4E86;Element&#x6811;&#x4E0A;&#xFF0C;&#x8FD9;&#x53EF;&#x4EE5;&#x6781;&#x5927;&#x7684;&#x964D;&#x4F4E;&#x590D;&#x6742;&#x5EA6;&#xFF0C;&#x63D0;&#x9AD8;&#x5F00;&#x53D1;&#x6548;&#x7387;&#x3002;&#x4F46;&#x662F;&#x4E86;&#x89E3;Element&#x5BF9;&#x7406;&#x89E3;&#x6574;&#x4E2A;Flutter UI&#x6846;&#x67B6;&#x662F;&#x81F3;&#x5173;&#x91CD;&#x8981;&#x7684;&#xFF0C;Flutter&#x6B63;&#x662F;&#x901A;&#x8FC7;Element&#x8FD9;&#x4E2A;&#x7EBD;&#x5E26;&#x5C06;Widget&#x548C;RenderObject&#x5173;&#x8054;&#x8D77;&#x6765;&#xFF0C;&#x4E86;&#x89E3;Element&#x5C42;&#x4E0D;&#x4EC5;&#x4F1A;&#x5E2E;&#x52A9;&#x8BFB;&#x8005;&#x5BF9;Flutter UI&#x6846;&#x67B6;&#x6709;&#x4E2A;&#x6E05;&#x6670;&#x7684;&#x8BA4;&#x8BC6;&#xFF0C;&#x800C;&#x4E14;&#x4E5F;&#x4F1A;&#x63D0;&#x9AD8;&#x81EA;&#x5DF1;&#x7684;&#x62BD;&#x8C61;&#x80FD;&#x529B;&#x548C;&#x8BBE;&#x8BA1;&#x80FD;&#x529B;&#x3002;&#x53E6;&#x5916;&#x5728;&#x6709;&#x4E9B;&#x65F6;&#x5019;&#xFF0C;&#x6211;&#x4EEC;&#x5FC5;&#x987B;&#x5F97;&#x76F4;&#x63A5;&#x4F7F;&#x7528;Element&#x5BF9;&#x8C61;&#x6765;&#x5B8C;&#x6210;&#x4E00;&#x4E9B;&#x64CD;&#x4F5C;&#xFF0C;&#x6BD4;&#x5982;&#x83B7;&#x53D6;&#x4E3B;&#x9898;Theme&#x6570;&#x636E;&#xFF0C;&#x5177;&#x4F53;&#x7EC6;&#x8282;&#x5C06;&#x5728;&#x4E0B;&#x6587;&#x4ECB;&#x7ECD;&#x3002;</p>
<h3 id="buildcontext">BuildContext</h3>
<p>&#x65E0;&#x8BBA;&#x662F;StatelessWidget&#x548C;StatefulWidget&#x7684;build&#x65B9;&#x6CD5;&#x90FD;&#x4F1A;&#x4F20;&#x4E00;&#x4E2A;BuildContext&#x5BF9;&#x8C61;&#xFF1A;</p>
<pre class="language-"><code class="lang-dart">Widget <span class="token function">build</span><span class="token punctuation">(</span>BuildContext context<span class="token punctuation">)</span> <span class="token punctuation">{</span><span class="token punctuation">}</span>
</code></pre>
<p>&#x6211;&#x4EEC;&#x77E5;&#x9053;&#xFF0C;&#x5728;&#x5F88;&#x591A;&#x65F6;&#x5019;&#x6211;&#x4EEC;&#x90FD;&#x9700;&#x8981;&#x4F7F;&#x7528;&#x8FD9;&#x4E2A;<code>context</code> &#x505A;&#x4E00;&#x4E9B;&#x4E8B;&#xFF0C;&#x6BD4;&#x5982;&#xFF1A;</p>
<pre class="language-"><code class="lang-dart">Theme<span class="token punctuation">.</span><span class="token function">of</span><span class="token punctuation">(</span>context<span class="token punctuation">)</span> <span class="token comment">//&#x83B7;&#x53D6;&#x4E3B;&#x9898;</span>
Navigator<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span>context<span class="token punctuation">,</span> route<span class="token punctuation">)</span> <span class="token comment">//&#x5165;&#x6808;&#x65B0;&#x8DEF;&#x7531;</span>
Localizations<span class="token punctuation">.</span><span class="token function">of</span><span class="token punctuation">(</span>context<span class="token punctuation">,</span> type<span class="token punctuation">)</span> <span class="token comment">//&#x83B7;&#x53D6;Local</span>
context<span class="token punctuation">.</span>size <span class="token comment">//&#x83B7;&#x53D6;&#x4E0A;&#x4E0B;&#x6587;&#x5927;&#x5C0F;</span>
context<span class="token punctuation">.</span><span class="token function">findRenderObject</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token comment">//&#x67E5;&#x627E;&#x5F53;&#x524D;&#x6216;&#x6700;&#x8FD1;&#x7684;&#x4E00;&#x4E2A;&#x7956;&#x5148;RenderObject</span>
</code></pre>
<p>&#x90A3;&#x4E48;BuildContext&#x5230;&#x5E95;&#x662F;&#x4EC0;&#x4E48;&#x5462;&#xFF0C;&#x67E5;&#x770B;&#x5176;&#x5B9A;&#x4E49;&#xFF0C;&#x53D1;&#x73B0;&#x5176;&#x662F;&#x4E00;&#x4E2A;&#x62BD;&#x8C61;&#x63A5;&#x53E3;&#x7C7B;&#xFF1A;</p>
<pre class="language-"><code class="lang-dart"><span class="token keyword">abstract</span> <span class="token keyword">class</span> <span class="token class-name">BuildContext</span> <span class="token punctuation">{</span>
    <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token punctuation">}</span>
</code></pre>
<p>&#x90A3;StatelessWidget&#x548C;StatefulWidget&#x7684;build&#x65B9;&#x6CD5;&#x4F20;&#x5165;&#x7684;context&#x5BF9;&#x8C61;&#x662F;&#x54EA;&#x4E2A;&#x5B9E;&#x73B0;&#x4E86;BuildContext&#x7684;&#x7C7B;&#x3002;&#x6211;&#x4EEC;&#x987A;&#x85E4;&#x6478;&#x74DC;&#xFF0C;&#x53D1;&#x73B0;&#x8C03;&#x7528;&#x65F6;&#x53D1;&#x751F;&#x5728;StatelessWidget&#x548C;StatefulWidget&#x5BF9;&#x5E94;&#x7684;StatelessElement&#x548C;StatefulElement&#x7684;build&#x65B9;&#x6CD5;&#x4E2D;&#xFF0C;&#x4EE5;StatelessElement&#x4E3A;&#x4F8B;&#xFF1A;</p>
<pre class="language-"><code class="lang-dart">
<span class="token keyword">class</span> <span class="token class-name">StatelessElement</span> <span class="token keyword">extends</span> <span class="token class-name">ComponentElement</span> <span class="token punctuation">{</span>
  <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
  <span class="token metadata symbol">@override</span>
  Widget <span class="token function">build</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">=</span><span class="token operator">&gt;</span> widget<span class="token punctuation">.</span><span class="token function">build</span><span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token punctuation">}</span>
</code></pre>
<p>&#x53D1;&#x73B0;build&#x4F20;&#x9012;&#x7684;&#x662F;this&#xFF0C;&#x5F88;&#x660E;&#x663E;&#x4E86;&#xFF0C;&#x8FD9;&#x4E2A;BuildContext&#x5F88;&#x53EF;&#x80FD;&#x5C31;&#x662F;Element&#x7C7B;&#xFF0C;&#x67E5;&#x770B;Element&#x7C7B;&#x5B9A;&#x4E49;&#xFF0C;&#x53D1;&#x73B0;Element&#x7C7B;&#x679C;&#x7136;&#x5B9E;&#x73B0;&#x4E86;BuildContext&#x63A5;&#x53E3;:</p>
<pre class="language-"><code class="lang-dart"><span class="token keyword">class</span> <span class="token class-name">Element</span> <span class="token keyword">extends</span> <span class="token class-name">DiagnosticableTree</span> <span class="token keyword">implements</span> <span class="token class-name">BuildContext</span> <span class="token punctuation">{</span>
    <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token punctuation">}</span>
</code></pre>
<p>&#x81F3;&#x6B64;&#x771F;&#x76F8;&#x5927;&#x767D;&#xFF0C;BuildContext&#x5C31;&#x662F;Widget&#x5BF9;&#x5E94;&#x7684;Element&#xFF0C;&#x6240;&#x4EE5;&#x6211;&#x4EEC;&#x53EF;&#x4EE5;&#x901A;&#x8FC7;context&#x5728;StatelessWidget&#x548C;StatefulWidget&#x7684;build&#x65B9;&#x6CD5;&#x4E2D;&#x76F4;&#x63A5;&#x8BBF;&#x95EE;Element&#x5BF9;&#x8C61;&#x3002;&#x6211;&#x4EEC;&#x83B7;&#x53D6;&#x4E3B;&#x9898;&#x6570;&#x636E;&#x7684;&#x4EE3;&#x7801;<code>Theme.of(context)</code>&#x5185;&#x90E8;&#x6B63;&#x662F;&#x8C03;&#x7528;&#x4E86;Element&#x7684;<code>inheritFromWidgetOfExactType()</code>&#x65B9;&#x6CD5;&#x3002;</p>
<blockquote>
<p>&#x601D;&#x8003;&#x9898;&#xFF1A;&#x4E3A;&#x4EC0;&#x4E48;build&#x65B9;&#x6CD5;&#x7684;&#x53C2;&#x6570;&#x4E0D;&#x5B9A;&#x4E49;&#x6210;Element&#x5BF9;&#x8C61;&#xFF0C;&#x800C;&#x8981;&#x5B9A;&#x4E49;&#x6210;BuildContext ?</p>
</blockquote>
<h3 id="&#x8FDB;&#x9636;">&#x8FDB;&#x9636;</h3>
<p>&#x6211;&#x4EEC;&#x53EF;&#x4EE5;&#x770B;&#x5230;Element&#x662F;Flutter UI&#x6846;&#x67B6;&#x5185;&#x90E8;&#x8FDE;&#x63A5;Widget&#x548C;RenderObject&#x7684;&#x7EBD;&#x5E26;&#xFF0C;&#x5927;&#x591A;&#x6570;&#x65F6;&#x5019;&#x5F00;&#x53D1;&#x8005;&#x53EA;&#x9700;&#x8981;&#x5173;&#x6CE8;Widget&#x5C42;&#x5373;&#x53EF;&#xFF0C;&#x4F46;&#x662F;Widget&#x5C42;&#x6709;&#x65F6;&#x5019;&#x5E76;&#x4E0D;&#x80FD;&#x5B8C;&#x5168;&#x5C4F;&#x853D;Element&#x7EC6;&#x8282;&#xFF0C;&#x6240;&#x4EE5;Framework&#x5728;StatelessWidget&#x548C;StatefulWidget&#x4E2D;&#x901A;&#x8FC7;build&#x65B9;&#x6CD5;&#x53C2;&#x6570;&#x5C06;Element&#x5BF9;&#x8C61;&#x4E5F;&#x4F20;&#x9012;&#x7ED9;&#x4E86;&#x5F00;&#x53D1;&#x8005;&#xFF0C;&#x8FD9;&#x6837;&#x4FBF;&#x53EF;&#x4EE5;&#x5728;&#x9700;&#x8981;&#x65F6;&#x76F4;&#x63A5;&#x64CD;&#x4F5C;Element&#x5BF9;&#x8C61;&#x3002;&#x90A3;&#x4E48;&#x73B0;&#x5728;&#x7B14;&#x8005;&#x63D0;&#x4E24;&#x4E2A;&#x95EE;&#x9898;&#xFF0C;&#x8BF7;&#x8BFB;&#x8005;&#x5148;&#x81EA;&#x5DF1;&#x601D;&#x8003;&#x4E00;&#x4E0B;&#xFF1A;</p>
<ol>
<li>&#x5982;&#x679C;&#x6CA1;&#x6709;Widget&#x5C42;&#xFF0C;&#x5355;&#x9760;Element&#x5C42;&#x662F;&#x5426;&#x53EF;&#x4EE5;&#x642D;&#x5EFA;&#x8D77;&#x4E00;&#x4E2A;&#x53EF;&#x7528;&#x7684;UI&#x6846;&#x67B6;&#xFF1F;&#x5982;&#x679C;&#x53EF;&#x4EE5;&#x5E94;&#x8BE5;&#x662F;&#x4EC0;&#x4E48;&#x6837;&#x5B50;&#xFF1F;</li>
<li>Flutter UI&#x6846;&#x67B6;&#x80FD;&#x4E0D;&#x505A;&#x6210;&#x54CD;&#x5E94;&#x5F0F;&#x5417;&#xFF1F;</li>
</ol>
<p>&#x5BF9;&#x4E8E;&#x95EE;&#x9898;1&#xFF0C;&#x7B54;&#x6848;&#x5F53;&#x7136;&#x662F;&#x80AF;&#x5B9A;&#x7684;&#xFF0C;&#x56E0;&#x4E3A;&#x6211;&#x4EEC;&#x4E4B;&#x524D;&#x8BF4;&#x8FC7;Widget&#x6811;&#x53EA;&#x662F;Element&#x6811;&#x7684;&#x6620;&#x5C04;&#xFF0C;&#x6211;&#x4EEC;&#x5B8C;&#x5168;&#x53EF;&#x4EE5;&#x76F4;&#x63A5;&#x901A;&#x8FC7;Element&#x6765;&#x642D;&#x5EFA;&#x4E00;&#x4E2A;UI&#x6846;&#x67B6;&#x3002;&#x4E0B;&#x9762;&#x4E3E;&#x4E00;&#x4E2A;&#x4F8B;&#x5B50;&#xFF1A;</p>
<p>&#x6211;&#x4EEC;&#x901A;&#x8FC7;&#x7EAF;&#x7CB9;&#x7684;Element&#x6765;&#x6A21;&#x62DF;&#x4E00;&#x4E2A;StatefulWidget&#x7684;&#x529F;&#x80FD;&#xFF0C;&#x5047;&#x8BBE;&#x6709;&#x4E00;&#x4E2A;&#x9875;&#x9762;&#xFF0C;&#x8BE5;&#x9875;&#x9762;&#x6709;&#x4E00;&#x4E2A;&#x6309;&#x94AE;&#xFF0C;&#x6309;&#x94AE;&#x7684;&#x6587;&#x672C;&#x662F;1-9 9&#x4E2A;&#x6570;&#xFF0C;&#x70B9;&#x51FB;&#x4E00;&#x6B21;&#x6309;&#x94AE;&#xFF0C;&#x5219;&#x5BF9;9&#x4E2A;&#x6570;&#x968F;&#x673A;&#x6392;&#x4E00;&#x6B21;&#x5E8F;&#xFF0C;&#x4EE3;&#x7801;&#x5982;&#x4E0B;&#xFF1A;</p>
<pre class="language-"><code class="lang-dart"><span class="token keyword">class</span> <span class="token class-name">HomeView</span> <span class="token keyword">extends</span> <span class="token class-name">ComponentElement</span><span class="token punctuation">{</span>
  <span class="token function">HomeView</span><span class="token punctuation">(</span>Widget widget<span class="token punctuation">)</span> <span class="token punctuation">:</span> <span class="token keyword">super</span><span class="token punctuation">(</span>widget<span class="token punctuation">)</span><span class="token punctuation">;</span>
  String text <span class="token operator">=</span> <span class="token string">&quot;123456789&quot;</span><span class="token punctuation">;</span>

  <span class="token metadata symbol">@override</span>
  Widget <span class="token function">build</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    Color primary<span class="token operator">=</span>Theme<span class="token punctuation">.</span><span class="token function">of</span><span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">)</span><span class="token punctuation">.</span>primaryColor<span class="token punctuation">;</span> <span class="token comment">//1</span>
    <span class="token keyword">return</span> <span class="token function">GestureDetector</span><span class="token punctuation">(</span>
      child<span class="token punctuation">:</span> <span class="token function">Center</span><span class="token punctuation">(</span>
        child<span class="token punctuation">:</span> <span class="token function">FlatButton</span><span class="token punctuation">(</span>
          child<span class="token punctuation">:</span> <span class="token function">Text</span><span class="token punctuation">(</span>text<span class="token punctuation">,</span> style<span class="token punctuation">:</span> <span class="token function">TextStyle</span><span class="token punctuation">(</span>color<span class="token punctuation">:</span> primary<span class="token punctuation">)</span><span class="token punctuation">,</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
          onPressed<span class="token punctuation">:</span> <span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
            <span class="token keyword">var</span> t <span class="token operator">=</span> text<span class="token punctuation">.</span><span class="token function">split</span><span class="token punctuation">(</span><span class="token string">&quot;&quot;</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token function">shuffle</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
            text <span class="token operator">=</span> t<span class="token punctuation">.</span><span class="token function">join</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
            <span class="token function">markNeedsBuild</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//&#x70B9;&#x51FB;&#x540E;&#x5C06;&#x8BE5;Element&#x6807;&#x8BB0;&#x4E3A;dirty&#xFF0C;Element&#x5C06;&#x4F1A;rebuild</span>
          <span class="token punctuation">}</span><span class="token punctuation">,</span>
        <span class="token punctuation">)</span><span class="token punctuation">,</span>
      <span class="token punctuation">)</span><span class="token punctuation">,</span>
    <span class="token punctuation">)</span><span class="token punctuation">;</span>
  <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<ul>
<li>&#x4E0A;&#x9762;build&#x65B9;&#x6CD5;&#x4E0D;&#x63A5;&#x6536;&#x53C2;&#x6570;&#xFF0C;&#x8FD9;&#x4E00;&#x70B9;&#x548C;&#x5728;StatelessWidget&#x548C;StatefulWidget&#x4E2D;build(BuildContext)&#x65B9;&#x6CD5;&#x4E0D;&#x540C;&#x3002;&#x4EE3;&#x7801;&#x4E2D;&#x9700;&#x8981;&#x7528;&#x5230;BuildContext&#x7684;&#x5730;&#x65B9;&#x76F4;&#x63A5;&#x7528;<code>this</code>&#x4EE3;&#x66FF;&#x5373;&#x53EF;&#xFF0C;&#x5982;&#x4EE3;&#x7801;&#x6CE8;&#x91CA;1&#x5904;<code>Theme.of(this)</code>&#x53C2;&#x6570;&#x76F4;&#x63A5;&#x4F20;<code>this</code>&#x5373;&#x53EF;&#xFF0C;&#x56E0;&#x4E3A;&#x5F53;&#x524D;&#x5BF9;&#x8C61;&#x672C;&#x8EAB;&#x5C31;&#x662F;Element&#x5B9E;&#x4F8B;&#x3002;</li>
<li><p>&#x5F53;<code>text</code>&#x53D1;&#x751F;&#x6539;&#x53D8;&#x65F6;&#xFF0C;&#x6211;&#x4EEC;&#x8C03;&#x7528;<code>markNeedsBuild()</code>&#x65B9;&#x6CD5;&#x5C06;&#x5F53;&#x524D;Element&#x6807;&#x8BB0;&#x4E3A;dirty&#x5373;&#x53EF;&#xFF0C;&#x6807;&#x8BB0;&#x4E3A;dirty&#x7684;Element&#x4F1A;&#x5728;&#x4E0B;&#x4E00;&#x5E27;&#x4E2D;&#x91CD;&#x5EFA;&#x3002;&#x5B9E;&#x9645;&#x4E0A;&#xFF0C;<code>State.setState()</code>&#x5728;&#x5185;&#x90E8;&#x4E5F;&#x662F;&#x8C03;&#x7528;&#x7684;<code>markNeedsBuild()</code>&#x65B9;&#x6CD5;&#x3002;</p>
</li>
<li><p>&#x4E0A;&#x9762;&#x4EE3;&#x7801;&#x4E2D;build&#x65B9;&#x6CD5;&#x8FD4;&#x56DE;&#x7684;&#x4ECD;&#x7136;&#x662F;&#x4E00;&#x4E2A;Widget&#xFF0C;&#x8FD9;&#x662F;&#x7531;&#x4E8E;Flutter&#x6846;&#x67B6;&#x4E2D;&#x5DF2;&#x7ECF;&#x6709;&#x4E86;Widget&#x8FD9;&#x4E00;&#x5C42;&#xFF0C;&#x5E76;&#x4E14;&#x7EC4;&#x4EF6;&#x5E93;&#x90FD;&#x5DF2;&#x7ECF;&#x662F;&#x4EE5;Widget&#x7684;&#x5F62;&#x5F0F;&#x63D0;&#x4F9B;&#x4E86;&#xFF0C;&#x5982;&#x679C;&#x5728;Flutter&#x6846;&#x67B6;&#x4E2D;&#x6240;&#x6709;&#x7EC4;&#x4EF6;&#x90FD;&#x50CF;&#x793A;&#x4F8B;&#x7684;HomeView&#x4E00;&#x6837;&#x4EE5;Element&#x5F62;&#x5F0F;&#x63D0;&#x4F9B;&#xFF0C;&#x90A3;&#x4E48;&#x5C31;&#x53EF;&#x4EE5;&#x7528;&#x7EAF;Element&#x6765;&#x6784;&#x5EFA;UI&#x4E86;&#xFF0C;HomeView&#x7684;build&#x65B9;&#x6CD5;&#x8FD4;&#x56DE;&#x503C;&#x7C7B;&#x578B;&#x5C31;&#x53EF;&#x4EE5;&#x662F;Element&#x4E86;&#x3002;</p>
</li>
</ul>
<p>&#x5982;&#x679C;&#x6211;&#x4EEC;&#x9700;&#x8981;&#x5C06;&#x4E0A;&#x9762;&#x4EE3;&#x7801;&#x5728;&#x73B0;&#x6709;Flutter&#x6846;&#x67B6;&#x4E2D;&#x8DD1;&#x8D77;&#x6765;&#xFF0C;&#x90A3;&#x4E48;&#x8FD8;&#x662F;&#x5F97;&#x63D0;&#x4F9B;&#x4E00;&#x4E2A;&#x201D;&#x9002;&#x914D;&#x5668;&#x201C;Widget&#x5C06;HomeView&#x7ED3;&#x5408;&#x5230;&#x73B0;&#x6709;&#x6846;&#x67B6;&#x4E2D;&#xFF0C;&#x4E0B;&#x9762;CustomHome&#x5C31;&#x76F8;&#x5F53;&#x4E8E;&#x201D;&#x9002;&#x914D;&#x5668;&#x201C;&#xFF1A;</p>
<pre class="language-"><code class="lang-dart"><span class="token keyword">class</span> <span class="token class-name">CustomHome</span> <span class="token keyword">extends</span> <span class="token class-name">Widget</span> <span class="token punctuation">{</span>
  <span class="token metadata symbol">@override</span>
  Element <span class="token function">createElement</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">return</span> <span class="token function">HomeView</span><span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<p>&#x73B0;&#x5728;&#x5C31;&#x53EF;&#x4EE5;&#x5C06;CustomHome&#x6DFB;&#x52A0;&#x5230;Widget&#x6811;&#x4E86;&#xFF0C;&#x6211;&#x4EEC;&#x5728;&#x4E00;&#x4E2A;&#x65B0;&#x8DEF;&#x7531;&#x9875;&#x521B;&#x5EFA;&#x5B83;&#xFF0C;&#x6700;&#x7EC8;&#x6548;&#x679C;&#x5982;&#x4E0B;&#xFF1A;</p>
<p><img src="https://cdn.jsdelivr.net/gh/flutterchina/flutter-in-action/docs/imgs/Screenshot_1547041690.png" alt="Screenshot_1547041690"> <img src="https://cdn.jsdelivr.net/gh/flutterchina/flutter-in-action/docs/imgs/Screenshot_1547041693.png" alt="Screenshot_1547041693"></p>
<p>&#x70B9;&#x51FB;&#x6309;&#x94AE;&#x5219;&#x6309;&#x94AE;&#x6587;&#x672C;&#x4F1A;&#x968F;&#x673A;&#x6392;&#x5E8F;&#x3002;</p>
<p>&#x5BF9;&#x4E8E;&#x95EE;&#x9898;2&#xFF0C;&#x7B54;&#x6848;&#x5F53;&#x7136;&#x4E5F;&#x662F;&#x80AF;&#x5B9A;&#x7684;&#xFF0C;Flutter engine&#x63D0;&#x4F9B;&#x7684;dart API&#x662F;&#x539F;&#x59CB;&#x4E14;&#x72EC;&#x7ACB;&#x7684;&#xFF0C;&#x8FD9;&#x4E2A;&#x4E0E;&#x64CD;&#x4F5C;&#x7CFB;&#x7EDF;&#x63D0;&#x4F9B;&#x7684;API&#x7C7B;&#x4F3C;&#xFF0C;&#x4E0A;&#x5C42;UI&#x6846;&#x67B6;&#x8BBE;&#x8BA1;&#x6210;&#x4EC0;&#x4E48;&#x6837;&#x5B8C;&#x5168;&#x53D6;&#x51B3;&#x4E8E;&#x8BBE;&#x8BA1;&#x8005;&#xFF0C;&#x5B8C;&#x5168;&#x53EF;&#x4EE5;&#x5C06;UI&#x6846;&#x67B6;&#x8BBE;&#x8BA1;&#x6210;Android&#x98CE;&#x683C;&#x6216;iOS&#x98CE;&#x683C;&#xFF0C;&#x4F46;&#x8FD9;&#x4E9B;&#x4E8B;Google&#x4E0D;&#x4F1A;&#x518D;&#x53BB;&#x505A;&#xFF0C;&#x6211;&#x4EEC;&#x4E5F;&#x6CA1;&#x5FC5;&#x8981;&#x518D;&#x53BB;&#x641E;&#x8FD9;&#x4E00;&#x5957;&#xFF0C;&#x8FD9;&#x662F;&#x56E0;&#x4E3A;&#x54CD;&#x5E94;&#x5F0F;&#x7684;&#x601D;&#x60F3;&#x672C;&#x8EAB;&#x662F;&#x5F88;&#x68D2;&#x7684;&#xFF0C;&#x4E4B;&#x6240;&#x4EE5;&#x63D0;&#x51FA;&#x8FD9;&#x4E2A;&#x95EE;&#x9898;&#xFF0C;&#x662F;&#x56E0;&#x4E3A;&#x7B14;&#x8005;&#x8BA4;&#x4E3A;&#x505A;&#x4E0E;&#x4E0D;&#x505A;&#x662F;&#x4E00;&#x56DE;&#x4E8B;&#xFF0C;&#x4F46;&#x77E5;&#x9053;&#x80FD;&#x4E0D;&#x80FD;&#x505A;&#x662F;&#x53E6;&#x4E00;&#x56DE;&#x4E8B;&#xFF0C;&#x8FD9;&#x80FD;&#x53CD;&#x6620;&#x51FA;&#x6211;&#x4EEC;&#x5BF9;&#x77E5;&#x8BC6;&#x7684;&#x638C;&#x63E1;&#x7A0B;&#x5EA6;&#x3002;</p>
<h3 id="&#x603B;&#x7ED3;">&#x603B;&#x7ED3;</h3>
<p>&#x672C;&#x8282;&#x8BE6;&#x7EC6;&#x7684;&#x4ECB;&#x7ECD;&#x4E86;Element&#x7684;&#x751F;&#x547D;&#x5468;&#x671F;&#xFF0C;&#x4EE5;&#x53CA;&#x5B83;&#x4E0E;Widget&#x3001;BuildContext&#x7684;&#x5173;&#x7CFB;&#xFF0C;&#x4E5F;&#x4ECB;&#x7ECD;&#x4E86;Element&#x5728;Flutter UI&#x7CFB;&#x7EDF;&#x4E2D;&#x7684;&#x89D2;&#x8272;&#x548C;&#x4F5C;&#x7528;&#xFF0C;&#x6211;&#x4EEC;&#x5C06;&#x5728;&#x4E0B;&#x4E00;&#x8282;&#x4ECB;&#x7ECD;Flutter UI&#x7CFB;&#x7EDF;&#x4E2D;&#x53E6;&#x4E00;&#x4E2A;&#x91CD;&#x8981;&#x7684;&#x89D2;&#x8272;RenderObject&#x3002;</p>

                                
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